Power over Ethernet (PoE), in accordance with both IEEE 802.3af-2003 and IEEE 802.3at-2009, each published by the Institute of Electrical and Electronics Engineers, Inc., New York, the entire contents of which is incorporated herein by reference, defines delivery of power over a set of 2 twisted wire pairs without disturbing data communication. The aforementioned standards particularly provide for a power sourcing equipment (PSE) and a powered device (PD). The power sourcing equipment is configured to detect the PD by ascertaining a valid signature resistance, and to supply power over the 2 twisted wire pairs only after a valid signature resistance is actually detected.
U.S. patent Ser. No. 7,492,059 issued Feb. 17, 2009 to Peker et al, the entire contents of which is incorporated herein by reference is addressed to powering a PD over 4 twisted pairs. Such a technique provides for increased power as compared to either of the above mentioned standards, and is commercially available from Microsemi Corporation of Alisa Viejo, Calif.
The HD BaseT Alliance of Beaverton Oregon has published the HDBaseT Specification Version 1.1.0 which defines a high power standard utilizing twisted pair cabling, such as Category 5e (CAT 5e) or Category 6 (CAT 6) structured cabling as defined by ANSI/TIA/EIA-568-A. The specification provides for even higher power than the above mentioned IEEE 802.3at-2009 over each set of 2 pairs, with all 4 pairs utilized for powering, and allows for power over structured communication cabling from any of: a type 1 PSE, denoted hereinafter as a low power PSE; a type 2 PSE denoted hereinafter as a medium power PSE; a type 3 PSE, denoted hereinafter as a high power PSE; twin medium power PSEs; and twin high power PSEs.
Detection, in accordance with any of the above standards requires the supply of at least 2 voltage levels between the range of 2.8 volts and 10 volts, with a signature resistance of the PD determined based on a calculation of the actual voltage levels, or current, detected. The use of 2 voltage levels allows for determination of the signature resistance irrespective of the existence of a diode bridge, typically supplied at the input to the PD.
A plurality of techniques are thus available for providing power over Ethernet cabling such as CAT 5e or CAT 6. A PD with a particular power requirement may find itself connected to a PSE supporting a power requirement in excess of its needs, in which case it may be powered, or alternately to a PSE not supporting sufficient power to meet its requirements. Various schemes to identify the power available from the PSE are known, such as those described in U.S. Patent Application Publication S/N US 2011/0163605 A1 published Jul. 7, 2011 to Ronen, the entire contents of which is incorporated herein by reference.
Many PD manufacturers prefer to focus their engineering resources on the functional aspects of the PD and purchase a PD interface which is arranged to receive the PoE and act in accordance with one or more of the above described techniques, while providing a power output for use with the PD. The range of power limitations however leads to a situation where complex communication is required between the PD and the PD interface in order to determine if sufficient power is available from the PSE to actual power the PD.